As a prior art relating to the present invention, there is a digital broadcast receiver disclosed in Patent Document 1. To improve receiving performance by reducing influence of adjacent interfering waves on a digital broadcasting wave, the digital broadcast receiver alters a delay point which is a switching point in the automatic gain control between the automatic gain control of the RF (Radio Frequency) band and the automatic gain control of the IF (Intermediate Frequency) band.
When there is an interfering wave other than a channel through which a digital broadcasting wave (desired wave) is transmitted, there are some cases where a desired signal cannot be received normally because of suppression of the received level of the desired wave owing to the automatic gain control of the RF band. To solve the problem, a conventional technique such as that disclosed in the Patent Document 1 decides deterioration in receiving performance due to the interfering wave from the automatic gain control of the RF band, the automatic gain control of the IF band, a result of an FFT (Fast Fourier Transform), a C/N (Carrier to Noise) value and the number of errors, and alters the operating point of the automatic gain control amplifier of the RF band when confirming the deterioration in the receiving performance due to the interfering wave. The operation can reduce the suppression of the received level of the desired wave due to the automatic gain control of the RF band, thereby making it possible to receive the desired signal.
However, merely altering the operating point of the automatic gain control amplifier of the RF band is not enough and has a problem in that if the received signal of the digital broadcasting wave is influenced by fading and its received level varies, a post-stage circuit is liable to saturate.
The present invention is implemented to solve the foregoing problems. Therefore it is an object of the present invention to provide a digital broadcast receiver capable of reducing the deterioration in the receiving performance due to an interfering wave and fading by altering a time constant of automatic gain control of each of the RF band and IF band simultaneously with the alteration of the operating point of the automatic gain control amplifier of the RF band.